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## Radio frequency energy harvesting and storing in supercapacitors for wearable sensors

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The radio frequency energy harvesting (RF-EH) and storing solution proposed in this chapter allows for collecting only a small amount of energy. However, it is more stable than solar and wind power sources. In fact, RF-EH relies on ambient RF signals from communications systems; hence, it presents special characteristics not found in other types of energy sources. The amount of RF energy harvested depends on the schedules of the base stations from the telecommunication service, as well as on the fluctuations caused by multipath fading and shadowing. As such, this work introduces a novel energy-management algorithm whilst proposing a supercapacitor storing system that copes with these issues and allows for storing the energy harvested from the electromagnetic waves by means of N-stage Dickson voltage multiplier printed circuit board (PCB) boards (5 and 7 stages) optimized to guarantee the best conversion efficiency and output voltage. Since the objective is to harvest as much energy as possible from the electromagnetic spectrum, this work proposes an RF-EH prototype to harvest electromagnetic energy from the digital terrestrial television (DTT) frequency band (750-758 MHz). This band is chosen due to the potential arising from the wide/broad deployment of DTT in Portugal, which poses significant interest for EH. Regarding the supercapacitor storing system, the best electronic components as well as the most suitable values for the configuration parameters have been determined through an empirical approach for the RF-EH with supercapacitor storing system. As an ongoing work, we are addressing the possibility of using different RF-EH prototypes gathered in blocks that scavenge energy in the same or different frequency bands, where the sum of all the energy harvested from each prototype is stored in the supercapacitor-based storage system, is also being considered. Preliminary tests are very promising, as in a conference room, densely populated, with circa 300 people, the RF-EH system managed to build up and store energy even when mobile phones were not being used in the close proximity of the harvesting antennas.

Chapter Contents:

• 14.1 Introduction
• 14.1.1 Motivation
• 14.2 Self-sustainable devices
• 14.2.1 RF energy harvesting using 5-stage Dickson voltage multiplier
• 14.2.1.1 RF energy-harvesting circuits
• 14.2.1.2 Simulation and experimental results
• 14.2.2 Energy storage and supercapacitors
• 14.3 Design of the RF energy harvesting/storage system
• 14.3.1 Specifications
• 14.3.2 Characterization of traffic ambient scenarios
• 14.3.2.1 Low traffic ambient
• 14.3.2.2 High traffic ambient
• 14.3.3 Front end block
• 14.3.3.1 Specifications of the buck–boost converter
• 14.3.4 Storage system control software
• 14.3.5 Back-end block
• 14.4 Performance evaluation
• 14.4.1 Average charging voltage in Csuper-cap
• 14.4.2 Average charging voltage per cycle in Csuper-cap
• 14.4.3 Normalized charging voltage in Csuper-cap
• 14.4.4 Charging time of Csuper-cap with limited cycles
• 14.4.5 Charging time per cycle of Csuper-cap
• 14.4.6 Csuper-cap voltage variation per cycle
• 14.4.7 Time and cycles estimation to attain different Csuper-cap voltages without harvesting device
• 14.4.8 Time estimation to attain different Csuper-cap voltages (with voltages (with harvesting device)
• 14.4.9 Implications of supercapacitors in series or parallel configurations
• 14.4.10 Design of N-stage Dickson voltage multiplier for DTT band
• 14.4.11 Experimental results for the 5-and 7-stage Dickson voltage multipliers
• 14.4.12 Design of a half-wave dipole antenna for DTT band
• 14.4.13 Experimental results for the complete solution of the RF energy harvesting and storing system
• 14.4.14 Simultaneous multiband GSM and DTT RF energy harvester
• 14.6 Conclusions
• References

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Radio frequency energy harvesting and storing in supercapacitors for wearable sensors, Page 1 of 2

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